From the article, "The earliest people to call themselves Chinese, which means "people of the black hair", lived in the North China plain". Except Chinese is an English term coming from the Qin (Chin) dynasty. Chinese today use huaren or zhongguoren, neither of which originated at the time being discussed nor do they mean anything about black hair.
Perhaps it means that there was once a term that was about people with black hair - and this group later developed into a Chinese ethnic group such as the Han.